1. Field of the Invention
The present invention relates to the field of semiconductor memory cards that can be used to extend the memory available to a wide variety of electronic devices that capture or use electronic data. More specifically, the present invention relates to a memory card with enhanced testability so that upon failure, particularly a failure in the field, the card can be examined and tested so that the source of or reason for, the failure can be identified to improve the reliability and quality of subsequently manufactured cards.
2. Description of the Related Art
Memory cards are flat memory units that incorporate semiconductor memory in a casing called a skin. A memory card may be about the size of a postage stamp, a matchbook or a credit card. Memory cards also include electrical contacts or connectors so that the memory in the card can be connected to a device that captures or uses digital data, for example, a digital camera. In this way, memory cards provide primary or additional memory capacity for the host device in much the same way that floppy disks provide additional memory capacity for computers.
Memory cards are typically non-volatile, meaning that they do not require power to maintain the data stored on them. Memory cards are also solid-state, semiconductor devices. Consequently, there are no moving parts to skip or break down while the stored data is being retrieved. Memory cards offer relatively high storage capacity, recently 32 to 64 MB. Capacities of up to 128 MB and 256 MB are expected in the near future. Memory cards also provide fast data transfer rates, security features and easy storage of data given the small size of the cards.
Memory cards can be used with, for example, digital cameras, music players known as MP3 players, personal digital assistants, game machines, wireless telephones, digital voice recorders, printers and other computer peripherals. Memory cards can also be placed in adapters and interfaced with personal computers like other computer memory cards.
There are many examples of memory cards that conform to different standards. Examples of memory cards include Secure Digital (“SD”) memory cards made by Matsushita, Toshiba and SanDisk Corporation; Multi-Media Cards (“MMC”); SmartMedia™ or SSFDC made by Toshiba; CompactFlash™ (“CF”) cards produced by SanDisk Corporation and Memory Stick® produced by Sony Corporation. The standards for different types of cards are usually set by industry associations. Information about memory cards and the associations that establish standards can be found at the following websites: http://www.sdcard.org; http://www.compactflash.org; and http://www.ssfdc.or.jp/englishlindex.htm.
FIG. 1a illustrates a block diagram of a generalized memory card (100) during the process of manufacturing the card. As shown in FIG. 1a, the typical memory card (100) includes, of course, a memory unit (102). The bulk of the memory card's real estate is used by the memory unit (102). A controller (101) may also be provided for controlling the storing of data to and the retrieval of information from the memory unit (102).
A main interface (103) electrically connects the components on the card (100) with whatever host device the card (100) is being used with. The main interface (103) typically includes a number, e.g. eight, of pins or contact pads that are brought into contact with, and thus electrically connected to, the data lines of the host device (not shown).
The various elements of the memory card (100) are formed on a substrate (109). The substrate (109) may be a printed circuit board or a semiconductor chip. The elements of the memory card, particularly the memory unit or units can be formed or mounted on one or both sides of the substrate (109).
As shown in FIG. 1a, access to the memory unit (102), via the main interface (103) is through the controller (101). During manufacture, a second interface, called the test interface (104) is formed on the substrate (109). The test interface (104) provides a direct connection (106) to the memory unit (102) as well as a direct connection (105) to the controller (101). Consequently, the test interface (104) provides more direct access to the components of the memory card (100) than is provided through the main interface (103).
As the card (100) is completed, the test interface (104) of the card (100) can be inserted into a slot or socket of testing equipment, such as a test computer. The test computer can then access and test the various components on the card (100) to enhance quality and reliability.
Because each type of memory card (100) can be used with different devices, there must be some standard for, at least, the various types of cards. Consequently, as mentioned above, industry associations or particular manufacturers set various standards for types of memory cards.
As shown in FIG. 1a, the permissible length for the card (100) given the applicable standards is illustrated as length (107). In order to maximize the memory capacity of the card (100), as much of this length as possible may be devoted to the memory unit (102). In fact, as shown in FIG. 1a, the test interface (104) extends a length (108) beyond the allowed length (107) of the card.
Consequently, as shown in FIG. 1b, once testing of the card (100) is completed, the test interface (104) is severed from the card (100). Molding may then be used to complete the components on the card (100), and the card (100) is then encased in a casing (110) known as a “skin.” The skin may be made, for example, of plastic or metal.
Problems, however, may still arise on the card (100). For example, a connection on the card (100) may fail or become broken, memory cells in the memory unit (102) may malfunction, or the controller (101) may malfunction. Any of these malfunctions may be caused by defects in the manufacturing process. Additionally, if a new circuit design is being implemented in a card (100), there may be bugs in the design that have gone undiscovered until the design is implemented.
Consequently, it is extremely useful to card manufacturers to be able to ascertain the location and, ultimately, the cause of any failure in the card (100). However, once the card (100) has been encased in the skin (110) and placed in service, the test interface (104) is gone and the card can only be tested by less direct methods using the main interface (103). Thus, what is called a “field failure” or a failure of the card (100) in the field when it is in use, can be very difficult to diagnose.
Consequently, there is a need in the art for an improved means of testing memory cards and diagnosing memory card failures, particularly after the card has been placed in service, i.e. a field failure.